Combined Precipitation- and Temperature- Based Dry and Wet Spell Dynamics of the Sabarmati River, India

The alternations between dry and wet spells usually result in more severe agricultural catastrophes than single-hazard events, which adversely affect food security as well as substantial socioeconomic loss. The multi-seasonal aspects of wet and dry spells are underlined by the abrupt shift from drought to flood i.e., reduced water levels in reservoirs with limited water supply to excess water to damage grown crops in agriculture fields. Therefore, analysis of the abrupt changing patterns of precipitation and temperature from season to season is the major interest of this study. With the above perspectives, a Standardized Precipitation Temperature Index (SPTI) is developed to study the dry and wet spell dynamics of the Sabarmati river basin which is one of the major west-flowing rivers of India. A year is considered to be dry if the SPTI value is less than or equal to -0.5, and wet if the value is more than 0.5. The developed index is a multi-scalar drought index which is derived using the observed precipitation and temperature data from the India Meteorological Department (IMD) for a study period of 1979 to 2018. Further, the analysis is performed for four different Indian seasons namely, Pre-South-West Monsoon (P-SWM), South-West Monsoon (SWM), Post-South-West Monsoon (Po-SWM), and North-East Monsoon (NEM) which are considered the accumulated precipitation and temperature values of March to May, October to November, and December to February, respectively. The general classification of SPTI indicates extremely wet to extremely dry severity levels of a river. An increasing trend of a dry spell is observed in this analysis. The SPTI formulation is expected to define the dry and wet spell of a river realistically since it considers temperature and precipitation data. Additionally, compared to other accessible indices, SPTI is more versatile in choosing appropriate probability distribution functions, which is practical for a decision-maker. This study can further be extended for a futuristic representation of wet and dry spells to provide decisive insights to the climate experts, stakeholders and communities.